Short Message Service (SMS) is a standardized communication service typically used in mobile communication systems but may also be used in non-mobile communication devices. Using standardized communications protocols, SMS allows for the interchange of short text messages between communication devices. SMS text messaging has become the most widely used data application on the planet, with 2.4 billion active users, or 74% of all mobile phone subscribers sending and receiving text messages on their communication devices.
While remaining largely unchanged since its introduction, SMS has had some enhancements introduced to its basic service. For example, Enhanced Message Service (EMS) enabled mobile phone can send and receive messages containing special text formatting (such as bold or italic), animations, pictures, icons, sound effects and special ring tones. Messages that are originated as an EMS message may be sent to a communication device that does not support EMS. In such cases the EMS message will be displayed as a conventional SMS message. However, the message may be unreadable due to the presence of additional data that cannot be rendered by the device. Typically, EMS messages cannot be exchanged between communication devices belonging to subscribers of different service provider, as the EMS messages will frequently be dropped by the inter-carrier network or by the receiving carrier.
As another example of some of the enhancements introduced to basic SMS service, Multimedia Messaging Service (MMS) is a telecommunications standard for sending SMS messages which include multimedia objects (images, audio, video, rich text). MMS is an extension of the SMS standard, allowing for longer message lengths. In addition, MMS may utilize Wireless Application Protocols (WAP) to display the content. MMS' most popular use is found in the sending of photographs from camera-equipped handsets, although it is also popular as a method of delivering ringtones as well.
SMS, EMS and MMS messages may be sent from one user (a sender) to another (a recipient) as a point to point communication (SMS-PP) or from one user (sender) to many other users (recipients) as a broadcast message (SMS-CB). Messages addressed to a recipient are sent by the sender to a Short Message Service Center (SMSC). The SMSC provides a store-and-forward mechanism. After receiving the message, the SMSC stores the message until the recipient's communication device alerts the SMSC that the recipient's communication device has registered with a communication network. Once the SMSC has received the alert, the SMSC will forward the message to the recipient's communication device and thereby remove the message from the SMSC's local memory. If a recipient's communication device is not reachable (e.g., turned off, out of range), the SMSC queues the message for later retry of delivery. Some SMSCs also provide a forward-and-forget delivery mechanism where transmission is tried only once.
Both store-and-forward and forward-and-forget delivery mechanisms are considered a “best efforts” type delivery mechanism. Neither delivery mechanism guarantees that a message will actually be delivered to its intended recipient and delay or complete loss of a message is not uncommon, particularly when sending between networks.